<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        .box{
            width: 100px;
            height: 100px;
            font-size: 30px;
        }
        .red {
            background-color: red;
        }
        .green {
            background-color: green;
        }
    </style>
</head>
<body>
    <div class="red box">红色</div>
    <div class="green box">绿色</div>
    <div class="red box">红色</div>
</body>
</html>